-----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Peter Hercek Sent: Friday, November 09, 2007 9:19 AM To: glasgow-haskell-users@haskell.org Subject: Re: GHC 6.8.1 is impressive!
New ghc sped up my small app (~2000 lines) by ~38%. Nice job! Anyway, my application is a bit slower when compiled with -O2 compared to -01 only (both with ghc 6.6 and 6.8). Is that normal? I assume you meant -O1, not -01, in "compared to -01." :) It's certainly not necessarily abnormal. It is well known that one can create situations where optimizations have a negative impact. The interesting question is, what are the characteristics of this particular application that are atypical, and thus appear to cause atypical optimization behavior? This type of situation is similar to the situation sometimes seen with multi-processor machines. In most cases, if you add processors, you get better performance. In some cases the reverse results. This is because there is some overhead to multiprocessing, and if a program is structure in such a way that parallelism is impossible, the multiprocessor overhead decreases performance and thus, for that particular application, performance is decreased. To continue the analogy, in most cases one can make minor modifications that will allow the application to use available parallelism. It is likely that small modifications to your program would allow it to take advantages of the increased optimization provided by -O2. So, as I said, it will be very interesting to discover the reason for the behavior you are experiencing. It might point to ways to make small code modifications to your application to increase performance. It might point to ways to improve the optimization. That's all premature of course. We don't know enough, to cite one quick example we don't know whether the optimization behavior is related to ghc behavior or to gcc behavior (although, of course, even if it is related to gcc behavior there could be interesting code generation issues). It would be fun to discover the details. Seth Kurtzberg Software Engineer Specializing in Security, Reliability, and the Hardware/Software Interface Peter. Lennart Augustsson wrote: > I'd like to second that. 6.8 is quite an improvement. Well done! > _______________________________________________ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users _______________________________________________ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users